Mechanism of formation and monomolecular decomposition of aci-nitromethanes: a quantum-chemical study

A quantum-chemical study of the reactions of formation of aci-nitromethane (aci-NM) and aci-dinitromethane (aci-DNM) and their decomposition with elim ination of water was carried out. The methods employed were the ab initio R HF method with inclusion of electron correlation at the MP2 level of theory and the Dunning-Hay double zeta basis set augmented with polarization d-fu nctions on heavy-element atoms, the DFT approach at the B3LYP level, and th e semiempirical PM3 method. The formation of aci-NM and aci-DNM was found t o be the limiting stage of the mechanism under study. For DNM, the barrier to reaction is substantially lower than for NM. The estimates of the height s of the barriers to formation found from density functional calculations a t the B3LYP/6-311++G(dfp) level (258 U mol(-1) for aci-NM and 218.5 U mol(- 1) for aci-DNM) are thought to be the most reliable.